Sexual Accidents

My boyfriend and I were having sex, he was wearing a condom, but it broke. He didn't know it had broken and kept at it for a couple thrusts after he had finished inside me. We immediately bought Plan B. As far as I know, that's all the further actions I can take to make sure I don't become pregnant. This ap says I'm at a 3% risk of pregnancy today. Does anyone else have some suggestions as to other preventative measures that I can take? Thanks!